The present invention relates to a color image processing apparatus and, more particularly, to an improved color image processing apparatus with excellent color reproduction.
Conventionally, a color image processing apparatus has been used in which a color image is recorded on a recording paper in such a manner that; a color image on a photograph or a text is optically read out by separating it into red R, green G, and blue B; these colors are converted into recording colors such as yellow Y, cyan C, black K, and the (color reproducing or color correction); and the color image is recorded on a recording paper by electrophotographic color image processing equipment according to the converted colors.
FIG. 8 is a schematic illustration which shows how colors are discriminated by the above-described color image processing apparatus, wherein the apparatus discriminates between a chromatic color and an achromatic color. A cube in FIG. 2 illustrates color discrimination as follows. An axis indicated by arrow mark R represents the density of R, an axis indicated by arrow mark B represents the density of B, and an axis indicated by arrow mark G represents the density of G. Accordingly, the leftside down corner indicated by the mark R,G,B DENSITY MINIMUM where the density of R, G, and B is zero, represents white, and the rightside upper corner indicated by the mark R,G,B DENSITY MAXIMUM, where the density of R, G, and B is maximum, represents black. For that reason, the region which links white with black in the cube represents ah achromatic color (gray) and outside of this region represents chromatic colors.
Concerning the setting of the achromatic color region, there are reciprocal problems as follows.
(1) The achromatic color region is required to be as wide as possible so that color ghosting (unnecessary colors which appear at the edge of black letter image) can be reduced, wherein the color ghosting is caused by shear of color and chromatic aberrations when black letters are processed.
(2) The achromatic color region is required to be as narrow as possible so that low chroma colors (for instance brown, dark blue, purple, and the like) can be precisely reproduced when a color gradation picture is processed.
Since these reciprocities exist, a compromise used to be made between case (1) and case (2) by setting the achromatic color region in such a manner that both cases are allowable.
In spite of that, colors of low chroma have been unsatisfactory when a color gradation picture is processed, since low chroma portions have been reproduced in black since the achromatic color region has a predetermined range as explained above.
On the other hand, even when a black letter is reproduced, the result is unsatisfactory as color ghosting appears.